1. Field of the Invention
The present invention relates to a continuously variable automatic transmission and more particularly to a continuously variable automatic transmission whose overall width is shortened so as to be accommodated in a limited space of an engine room.
2. Prior Arts
In general, a continuously variable automatic transmission used for a motor vehicle comprises a continuously variable transmission which is a main transmission mechanism for controlling vehicle speeds during normal operation, a starting apparatus for controlling power transmission of an engine and transmission during a vehicle starting period, a forward and reverse changeover apparatus and a clutch for engaging and disengaging the forward and reverse changeover apparatus.
For example, Japanese Patent Application Laid-open No. Toku-Kai-Shou 61-105333 discloses a continuously variable automatic transmission using a torque converter as a starting apparatus, as shown in FIG. 2.
This continuously variable transmission 1 is constituted by a starting apparatus 2 directly connected with an engine "A" and including a torque converter 2a therein, a continuously variable transmission 3 and a forward and reverse changeover apparatus 4 provided between the starting apparatus 2 and the continuously variable transmission 3. The forward and reverse changeover apparatus 4 includes a double pinion type planetary gear 4a, a forward clutch 4b and a reverse brake 4c.
When the vehicle runs forward, the forward clutch 4b is engaged so as to rotate the planetary gear 4a integrally with the torque converter 2a and as a result driving force is transmitted directly from the torque converter 2a to a primary pulley 3a of the continuously variable transmission 3. On the other hand, when the vehicle goes backward, the forward clutch is disengaged and at the same time the reverse brake 4c is engaged so as to fix the rotation of a ring gear of the planetary gear 4a and then a sun gear is rotated reversely with reduced speeds with respect to a carrier rotated by a clutch drum of the forward clutch 4b. As a result of the reverse rotation of the sun gear, the primary pulley 3a is rotated reversely.
FIG. 3 is an example of the case where the engine and the transmission are arranged transversely, in which the overall width "W" of the engine "A" and the transmission 1 must be a size to be able to be accommodated in an engine room.
Recent motor vehicles are equipped with a frame 7 in an engine room for absorbing an impact on both sides of the vehicle in case the vehicle has a collision from the lateral direction. Further, a front tire 8 is arranged outside of the frame 7.
The frame 7 must have some extent of a sectional area enough to maintain rigidity for the safety purpose and further the front tire 8 is required to move within as large steering angle as possible in order to obtain a small turning radius.
As a result of these, a space for accommodating the engine "A" and the transmission 1 in the engine room 6a tends to become small, therefore the overall width "W" of the engine and the transmission 1 should be shortened as far as possible.
However, in the continuously variable automatic transmission 1 of the prior art, since the starting apparatus 2 and the forward and reverse changeover apparatus 4 are arranged between the engine "A" and the continuously variable transmission 3 according to the order of the transmission of power, it is technically difficult to shorten the overall width "W'" of the continuously variable automatic transmission 1. Several means such as making a pulley ratio of the continuously variable transmission small, reducing the width of a belt wound around both pulleys, making walls thin, making clearances between components small and the like can be considered. However, any of these means have possibilities of incurring an adverse effect on function of the continuously variable automatic transmission 1 or incurring a lowering in rigidity and strength of the transmission.
Further, Japanese Patent Application Laid-open No. Toku-Kai-Hei 7-190164 discloses a technique in which the overall width of the continuously variable automatic transmission is shortened by means of abolishing a wall for separating a fixed sheave of the primary pulley from the forward and reverse changeover apparatus by supporting both fixed sheave and forward and reverse changeover apparatus with a common wall.
However, this technique has a possibility of exacerbating durability of components because of a long span of length between two bearings for supporting the fixed sheave.
Further, U.K. Published Patent Application No. 2033029 proposes a technique in which the overall width of the continuously variable automatic transmission is reduced by incorporating a single pinion type planetary gear into the inner periphery portion of the torque converter.
This prior technique, however, has a disadvantage that since the reverse brake is disposed on the transmission side, the carrier of the planetary gear must be interconnected with a rotary plate of the reverse brake through a sleeve. Because of this, not only the construction becomes complicated but also the overall width of the automatic transmission becomes long as much as the width of the reverse brake.